"When we first joined the show, [co-creator] JJ Abrams said that he thought it was a six-year show, but that's like saying you're going to climb Mount Everest," Noble told Allocine. "It's very hard to even [get a show] on, let alone to do six years."

Noble, who plays Walter Bishop, went on to say that while he expects Fringe to run for five years, he would be "surprised" if the show continued beyond that point.

"Six [years] is a very long time," he said. "But if we don't maintain the level of our production and our stories this [fourth] year, then there won't [even] be another year."

The actor also admitted that Fringe's complex storylines could discourage new viewers from watching the show.

"I think the fans have been amazing, but the bottom line of television is income," he said. "One of the issues with Fringe now is that you can't just turn [the show] on and watch it. In the first season, you could [do that] because it was more procedural."